The present embodiments relate to a method of forming a semiconductor device, and more particularly, to a method of forming a controlled dielectric stack on top of a semiconductor device.
In the present art, it is known that electromagnetic signals have important interactions with materials in a conventional CMOS process. Whether these signals be optical, in the form of guided or free-space light, or longer wavelength in nature, the control of dielectric constant, film thickness as well as the presence or lack thereof of metals in an associated semiconductor device is fundamental to ensuring device performance. Methods to improve the controllability of these physical layers serve to improve the manufacturability of any of such devices.
In one aspect, impinging radiation or guided radiation interacts with the back end dielectric stack of a conventional CMOS process. This radiation may be traveling along the wafer's surface through the dielectric, as in the case of a transmission line, or in another embodiment, it could be traveling normal to the film stack to interact with an underlying device. One such device is a grating coupler. Grating couplers on silicon are discussed in literature, wherein the grating couplers diffract light at normal incidence into a waveguide on a silicon surface. However, while such grating coupler structures have been theoretically simulated, they are not known to have been demonstrated in an optimized CMOS process manufacturing environment. In such a demonstration, the impinging radiation would need to travel through a highly uniform and controllable back-end dielectric stack to arrive at its destination, which may be in the form of a guided wave traveling perpendicular to the wafer's surface. Ideally, electromagnetic signal can not interact with parasitic metal. CMP non-uniformity resulting from the inability to use state-of-the-art metal tiling algorithms associated with such devices in the overlying ILD layers could reduce the efficiency of such devices.
Accordingly, it would be desirable to provide a method for manufacturing a semiconductor device, such as a grating coupler structure, an electromagnetic receiver or transmitter, or waveguide for overcoming aforementioned problems in the art.